Sorry to necro an old thread, but this thread is the first answer that pop up when search with Google and the correct answer is not here. Hopefully this will help someone down the road so they won't spend too much time looking for the answer like I did.
Go to the Setting in Google Now app. Press on Account & Privacy. Turn off "Open webpage in app". Now when you open a feed, it will be opened in external browser. If you happen to set Chrome as default external browser, then follow the instruction posted in the earlier replies to change to something else.